Laneryd, Tor

Wihlen, Malin

Abstract [en]

Dynamic transformer rating (DTR) can be used to load power transformers above nameplate rating, while respecting contingency loading limits and ensuring an acceptable risk level. Purchase of power transformers is a major contributor for high costs of building new substations. Application of DTR allows to postpone the investment in new power transformers in old substations, thus DTR has a potential to become an economically beneficial technology. A quantitative risk and economic evaluation of DTR application is performed for a wind farm connected transformer and thus for a highly variable load scenario. The risks analyzed in this project are increased loss of insulation life and the risk of dielectric failure, based on the Arrhenius-Weibull model. A comparative net present value calculation has been performed to investigate the profitability of replacing a 19.4 MVA transformer with a 16 MVA dynamically rated transformer. The feasibility of DTR application is analyzed and a methodology is developed to support both transformer manufacturer and potential customers, such as distribution system operators, in the decision-making process of purchasing of dynamically rated transformer for wind energy applications.

Morozovska, Kateryna

Abstract [en]

Dynamic Rating (DR) is usually associated with unlocking the capacity of power lines and transformers using available information on weather conditions. Our studies show that Dynamic Rating is a broad concept that requires further study and development.

The capacity of the majority of power devices is highly dependent on the heat transfer properties of the materials which the devices are made of. To ensure correct power limits of the equipment, one must take into consideration not only the power load, but also ambient conditions, such as: temperature, wind speed, wind direction, solar irradiation, humidity, pressure, radiation into the atmosphere and magnetic losses.

Dynamic rating is created as an alternative to standard constant rating that is designed with reference to extreme weather and load conditions. Some areas are more likely than others to experience extreme weather conditions, which have a chance of occurring only a few days per year for short periods of time. Such a distribution of weather parameters gives an opportunity to embed existing material properties of the power equipment and achieve a better utilization of the grid.

The following thesis is divided into two simultaneous topics: Dynamic line rating and Dynamic transformer rating. The division is motivated by the importance of analysing the operation of the above-mentioned parts of the power network in greater detail. Power lines and transformers play a significant part in grid planning and have a potential to result in economic benefits when used with DR.

The main focus of the doctoral project "Dynamic rating of power lines and transformers for wind energy integration" is on exploring potential ways to connect power generated from wind to the grid with the help of dynamic rating technologies. Therefore, great focus of the work lies on the analysis of DR connection of variable energy sources such as wind farms.

The thesis presents the comparison of different line rating methods and proposes a new way of their classification. Evaluation of dynamic line rating application has shown the possibility to expand the power grid with additional capacity from wind power generation. Literature analysis and detailed evaluation of the conductor heat balance models have led to experimental evaluation of the convective cooling effect.

The dynamic transformer rating application has shown a possibility to decrease the size of the power transformer without shortcoming in component availability.